Polyurethane foams are prepared by reacting, in the presence of a blowing agent, polyisocyanates with a high molecular weight polyol. Usually catalysts, such as organo-tin compounds and tertiary amines, and emulsifiers such as silicone oils are incorporated into the reaction mixture to control reaction rate, cell size and porosity.
In the prior art many efforts have been made to modify the properties of polyurethane foams and/or reduce the costs of producing such foams by adding various inert filler materials. For example, U.S. Pat. No. 3,298,976 discloses polyurethane foams prepared by adding the mineral filler barytes (e.g., barium sulfate) in finely divided form to the reaction mixture of the polyol and polyisocyanate and by using a lower amount of water. The mineral filler has an average particle size of 5 microns or greater and is added in an amount of from about 50 to 150 parts by weight based on 100 parts of the polyether polyol. The polyurethane foam is made either with a "one-shot" reaction method where the ingredients are reacted and simultaneously foamed, or in a "two-stage" method where the polyol is reacted with the polyisocyanate to form a partially reacted prepolymer, and subsequently an activator mixture (water and catalyst) is added to form the desired cellular polyurethane. The resultant filled virgin foams are stated to have good resilience and weight characteristics as compared to rubber latex foams.
Other filled virgin polyurethane foams are disclosed in U.S. Pat. No. 4,108,791. Such flexible polyurethane foams contain 0.1 to 5 percent by weight of an inorganic filler with particle sizes less than about 7 microns, including fumed silica, calcium carbonate, barium sulfate, aluminum silicate, kaolin, cadmium selenide, titanium dioxide, aluminum trihydrate, mica and iron oxide. The foams are stated to be readily molded without shrinkage. Further examples of filled virgin polyurethane foams are found in U.S. Pat. Nos. 4,452,920 and 3,598,772.
The present invention relates, however, to certain filled rebond polyurethane foams with desired foam density, plushness and other properties. Rebond polyurethane foam has been made in the prior art by shredding or grinding waste polyurethane foam to form polyurethane foam particles or chunks, mixing the polyurethane foam particles with a binder, placing the mixture into a mold, then curing the binder with steam.
Heretofore, when fabricating rebond foam it was generally possible to incorporate only relatively low amounts of solid materials into the rebond system to modify the rebond foam structure because the filler material would classify, agglomerate or settle out. As a result of the nonuniform distribution of large amounts of filler, the resultant rebond foam would have poor physical characteristics. One suggested method to incorporate more filler into a rebond foam product was to add the desired filler to the virgin foam, and then shred that virgin filled foam for use in the rebond product. U.S. Pat. No. 3,772,219 teaches a flexible polyurethane foam composition made by mixing 100 to 200 parts by weight of pulverulent limestone (calcium and magnesium carbonate) with 100 parts by weight polyether polyol and then mixing in the additional foam-forming reactants. The filled virgin foam so made can be shredded or chipped to smaller pieces and incorporated into a rebond foam. This method has limited utility because it is cost-prohibitive to make filled polyurethane foam solely for purposes of incorporating particles of that foam in a rebond product. Rather, rebond foam normally and preferably is formed with a broad range of scrap polyurethane foams.
The prior art does suggest that some fillers could be mixed with polyurethane foam chips before forming a new polyurethane foam structure with the chips and filler. For example, U.S. Pat. No. 4,438,221 discloses unique polyurethane foam-filled foams, in which a solid filler is mixed with shredded or ground polyurethane foam and this admixture is incorporated into the reaction product of a polyisocyanate and a reactive polyol. The '221 patent lists many possible fillers, including liquids and solids. Representative solids identified include graphite, carbon particles, metal filings, polymer powders, asbestos fibers, sawdust, pigments, soaps, detergents, beads, ground rubber, flame-retardant materials, but the patent only includes working examples in which solid flame-retardant materials were added as the solid material. In the '221 patent, the filler, shredded foam and reaction product are compressed in a mold through which steam is passed to foam the reaction product. A portion of the solid material (filler) penetrates into the foam chips, but the majority of the foam chips retain their original physical characteristics. The reaction product reacts with the water (steam) and forms a foam that adheres to the filler and the foam chips. For each 100 parts of pre-formed discrete polyurethane foam chips, there are from 40 to 200 parts of solid filler and 30 to 75 parts of reaction product or "new" foam binder. Unlike rebond foam structures in which a cured adhesive or binder coats some of the foam cell strands of the foam chips and holds the foam chips together, in the '221 patent, the foam chips are held together by a foam or foamed binder. In the '221 patent, the fillers are incorporated into and held within the foam particles of the newly formed foam (foamed reaction product). This filled foamed binder penetrates into the foam cell cavities of the scrap foam chips. In a sense cumulative to the patents teaching how to make filled virgin polyurethane foams, the '221 patent teaches how to disperse filler in a virgin polyurethane foam, which virgin foam is used to hold the other foam particles together to make the foam-filled foam structure. This patent does not show how to disperse fillers into a typical prepolymer binder for a rebond structure, a prepolymer binder that is cured with steam, but is not "foamed". This patent further does not show a rebond foam structure which has inert inorganic fillers uniformly distributed throughout the cured prepolymer binder (without either classifying or substantially penetrating into the foam chips) to improve the softness or plushness of the bonded foam at a given density.
Surprisingly, it has been found that certain inorganic mineral fillers, otherwise inert to the foam, such as barium sulfate, calcium carbonate, silica and talc, may be incorporated into a rebond polyurethane foam structure and uniformly distributed in the cured prepolymer binder of the rebond foam structure without penetrating into the foam strands of the foam particles. Such filled rebond polyurethane foam has an improved softness or plushness at a given density over unfilled rebond polyurethane foam.